Transmission control



Filed Dec. 24. 1923 25 paratus Patented Sept. 6v, 1927.

i .FRANK iafowAnn GRAHAM,

'raro COMPANY, Yoan.

INCORPOBATED, -OF NEW YORK,

OF BROOKLYN, NEW YORK, ASSIGNOR T' WESTERN lELEC- N. Y., A CORPORATION OF NEW TRANSMISSION coN'rnoL.

Application mea December 24, 1923. serai No. 682,507.

This invention relates to electric wave transmission and particularly to controlling the quantity and characteristic of transmission through a system. l

In .testing the hearing, more especially that of deaf persons, valuable information can be obtained by measuringthe sensitivity of the ear to a pluralityof pure tones extending` in pitch throughout the range of audibility. ,The normalrange of hearing with respect to both intensity and pitch has been determined by measurements on a large number of persons land has been charted and discussed by Fletcher in the Bell System l5 Technical Journal, Vol. I1,- No. 4, October, 1923, pages 145 to 180. In the same article, the author shows thatv the type of deafness as characterized by the responsiveness of the ear 'to tones of different pitches varies considerably amongst individuals and that considerable aid in the diagnosis of abnormal hearing maybe obtained from theresults' of such measurements. I

In accordance with this invention, an apfor ear analysis is provided whereby a large number of tones may be produced of known 'pitch and of variable energy, the

amount of which is known eitherv relatively or absolutely; l

In making tests to determine the intensity of sound energy corresponding to the limit of hearing, it is desirable, sincenthe limit may vary greatly for different pitches, to use a pure tone and also to prevent the possi- 35, bility of a lfrequency other than that desired for the particular test being produced by an' improper manipulation of the apparatus. A vacuum tube oscillator may be used as a dependable source of oscillation 410 energy for the production of pure tones .dif-

ferent pitches being secured by the use ofv a multiplicity of tuned circuits. The frequency of oscillation and hence the pitch of the tone may be controlled by a set of keys each one of which may be operated to connect a diHerent tuned circuit into the oscillator circuit. Further, in accordance with this invention these keys may be so inter connected' that whereas the' operation of any 5 one key by itself establishes oscillations of aparticular frequency the operation of two or more keys together' circuit in such a way that no oscillations can be generated. Accordingly, it is a parbreaks the oscillatorticular object of this invention to provide an apparatus for the generation of, pure tones delinitely determined-as to pitch and incapable of being operated tol produce a tone other than that desired.

`A further object of this invention is to creased precision in the determination of the threshold condition of audibility, or the degree of intensity as measured by the energy of the sound waves at which a tone becomes just audible. When the intensity of a tone is nearl the threshold value its audible ei'ect may, if the tone is continuous, be readily obscured by anything that may distract the attention of the subject, with the result that widely varying' results may be found. Interruption of the tone at intervals serves to aid attention of the subject and -so permit a more accuratedetermination of the limiting intensity. -It is necessary that the attention of the subject be directed sence of an audible tone and his judgment must not be aided'by the possibility of'his observing other effects concurrent with the interruption ofthe 'tone It is commonly lexclusively to judging the presence or ab-` 1 the case that in an electrical system for the production of audible tones the interruption of the electric current-produces an audible click due to the sudden discharge of energy storedin the reactive portions of the circuit.

The character of such a transient being greatly different from that of the steady tone its audibility is not in general related to thel audibility of the tone' and may persist after the threshold condition of the tone has been reached and passed'with the result that a false determination may be made. difficulty is avoided by causing the oscillations to be stopped by thevinterruption of a' non-reactive or substantially non-reactive branch of the oscillator circuit.

The above and other objects of the invention will be clearly understood from .the following detailed. description and claims This l'oo

taken in connection with the accompanying drawing in which Fig. l represents a complete `system embodying the invention and `Fig. 2 shows an alternative method of interrupting the tone by changing the resistance of the anode circuit of a vacuum tube oscillator. i

los

co provide in an apparatus for ear analysis inis delivered. 1

Referring to the drawing vby reference numerals 1 is an energy amplifyin device to be' described later in detail. T e electrodes 4 and 2 constitute terminals for the input of energy and electrodes 3 and 2 output terminals from which The amplifier y1 may be caused to generate oscillations in a manner that is well known and understood by feeding back to an in'put circuit connected to the input terminals part of the` energy delivered to an output circuit connected to the output terminals or electrodes 3 andy 2. The frequency of'the oscillations may be ldetermined by the constants ofa tuned circuit connected in either the output circuit -or the inputcircuit or mutually connectedto both.

In this invention selective networks 8 each comprising an inductance 9 and a condenser 10 are arranged to be connected one at a time to the amplifier 1 by means of keys 12, 13, 14 and 15. A plurality of oscillation circuits is thereby provided each having a tuned circuit connected in the amplifier output circuit in which oscillations are set up of a frequency determined by the constants i ofthe elements 9 and 10 vand from which energy is fed back to the input circuit by.

means of an inductively -coupled coil 11..

The constants of the various tuned circuits 9, 10 are adjusted so as '-to provide oscillations at frequencies corresponding to a series of tones extending through the range of audibility.

Ak parallel branch of the output circuit of of'produclnga large degree of attenuation.

It 1s also desirable that the degree of attenuation be "substantially independent of the frequency, for which reason it is `desirable to make the attenuator non-reactive at all frequencies. The form shown in the drawing is that 4described in the application of.4

R. L. Wegel vSerial Number 483,533, led July 9, 1921. In this form equal rcsistances A28 and 4equal resistances 29 are arranged to form a repeated ladder-like circuit structure the resistances 28being connected in series in one side of the circuit and the resistances 29 being connected in shunt across the circuit to al common lead 27 Contact points 25 are connected tothe junction points of the series and shunt resistances contact with any one of which may be made by an adjustamplified y energy able contact arm 26. If an electromotive i force is applied kto the terminals at vone end of this ladder-like circuit the potential difference between any contact point and the common lead 27 is readily determined from the values of the resistances and if the circuit had an infinitely great number of Sections the otentials of the successive contact points with respect to the common lead would be related to leach other as the terms of a geometric series, whereby the estimation of the potential differences corresponding to the various points is rendered sim le. The effect of an infinitelylprolongedlad er? like circuit' may be secured by making the resistance of the final shunt resistance 40 equal to i in WhichR1 is the resistance/of each series resistance element 28 and R2 the resistance of each shunt element 29. The proof of this may be demonstrated by the application of the formulae given in Patent No. 1,227113 patented to G. A. Campbell May 22, 191

Inithe apparatus of this invention energy from the transformer 18 is supplied to the attenuator and the receiver 24 is arranged to be connected through plug 23 and jack 22 to the contact arm 26 and the common lead 27. The fact that receivers of the type elnployed in this invention have a finlte'ilnpedance usually 'about 200 ohms makes it necessary that the resistances R1 and R2 be small in order that the geometric or logarithmic relationship between the potentials of the successive contacts be not seriously disturbed by the presence of the shunt path through the receiverz The effective resistance of the ladder-like network offeredA to the energy fromthe transformer 18 is equal to and .if thevalues lof R1 and R2 are so proportioned as to make this quantity equal tovabout 15 ohms it'is found that Lthe,'rela` tionship is maintained with sufficient accuracy.

The -method whereby .the generation of oscillations of improper frequencies is prevent-ed will now be described.

A common terminal of each'of the selective networks 8 is connected t'o a common lead which in-turn is connected to the electrode 2 of the amplifier common to -both output and input circuits. The other'terrninals of the inductance coils 11 and the tuned circuits 9,-10, are connected respectively to contact .elements 30 and 31 of the keys 12. 13, 14

and 15 one of which is associated with each network. When the keys are not operated selective networks are disconnected from the oscillator circuit. y

Associated in each key with contact element 3() are two contact elements 32 and 33 which are in Contact when the switch is not operated but which are separated when the keys are operated by the operating devices 16, contact then being made between the elements `30 and 32. Contact ele- `ments 34 and 35 are likewise associatedA with element 31 in each key, contact being made between the elements 34 and 35 when t-he keys are not operated and between 34 and 31 when the keys are operated.

A circuit connected to amplier electrode 4 is connected tothe transfer element 32 of key 12 an'd is continued from element 33 to Athe transfer element 32 of key 13 and so on passing through the various keys in the sequence 12," 13,- 14,- and 15,-?.

ln like manner a circuit starting from the output electrode 3 of the amplifier passes through the keys in the reverse sequence 15-14-13-12 including in each key the contact elements 34 and 35.

These two circuits may be terminated at the .last -keys of the sequence or they ni-ay be returned to the common electrode 2.

The operation of one of the keys, for example 13, separates the contacts between elements 32 and 33, and between elements 34 and 35 thereby' breaking the continuityof both of the above mentioned circuits. Further, the contacts of elements 32 and 34 are transferred respectively to elements 30 and 31 thereby connecting the selective circuit associated with key 13 to the input and output terminals of the amplifier and causing os-` cillations to be established. It will be noticed that the connection of the particular network selected by the key to the amplifier input and output terminals is established by two circuits one of which passes through all keys of lower numbers in the sequence and the other of whichA passes through all keys of higher numbersv in the sequence. Both circuits are essential to the sustaining of oscillations and consequently the operation of any one other key will sufiice to stop the oscillations. Further, since each key acts in a like manner with respect'to all of the others it is evident that oscillations can be generated only when one key and when one key only is operated.

From the foregoing description it is evident that a specific form of energy amplifying device is not essential to the operation of the invention but in the preferred form of the invention a three-electrode thermiouic vacuum tube is used, the electrodes 2, 3 and 4 being -respectively the cathode. anode and control electrode. The cathode consists of a filament heated by current from a battery 5 in a circuit connected to its terminals.

including the transformer 18 and the selective circuit 8.

Starting and stopping the oscillations is accomplished also by the operation of key 37 a resistance 39 being inserted in series with the heating battery 5 when the key contact is opened. The-resistance 39 is of such value as to reduce the heating current and hence also the temperature of the filament to a. point at which oscillations cannot be sustained. The lilament circuit is practically non-reactive so that there is no `discharge of stored energy at the instant the current is changed and consequently no noise producing transient. The attainment of this re sult is aided by the fact that the temperature of the filament changes relatively slowly thus preventing. any abrupt change 1n the oscillation amplitude. Two resistances 38 are connected 1n series across the terminalsI of the iilament and the common leads of the Referring to Figure 2, a resistance 39 is ounected in the common connection between the anode andthe selective circuits. This resistance is short circuited by a circuit through the contact of the key 3.7 and is inserted in the circuit by opening the key contact. Its value is made suiliciently large to stop the oscillation of any of the circuits so that by opening and closing the key circuit oscillations are stopped and started at will.

The anode circuit in which the resistance is inserted includes thespace discharge path within the vacuum tube, a resistance 36, the purpose of which will be described later, and a parallel tuned circuit 9 1() whose imlos pedance at resonance is high and practically purely resistive. The absence of reactance from this circuit results in freedom from stored energy therein which would be dissipated in anoise producingtransient at the moment of manipulating the key.

The resistances 36 connected in series with each tuned circuit are provided for an initial adjustment of the energy of the oscillations corresponding to each tone. It is desirable that for any given setting of the attenuator the energy convertedinto sound energy by the receiver 24 should be the same for eachk ceivver.

-be produced at different frequencies. It is necessary therefore that the efficiency of the receiver as a convertor of energy be known at the different frequencies of the oscillator.

Thismay be determined by comparing the receiver with a fundamental standard in which the conversion efficiency can be definitely determined from simple measurements. Such an apparatus is the thermophone described by Arnold and Crandall in the Physical Review, volume 10, number 1, July 1917. l 4

With the eiciency of the receiver deter- 1 mined atA the various frequencies the resistances 36 may be made of the correct value sov that the intensity of oscillationsat each frequency corresponds to a uniform' amount of sound Wave energy produced by the re- From the foregoing description the method of operation of .the invention is readily evident. l

The receiver 24 is connected into circuit by means of plug 23 and jack 22 and is aps plied to the ear, an analysis of which is,to be made. 4 One of keys 12-13-14-15 is operated connecting the corresponding tuned circuit into the oscillator circuit whereby'oscillations are started and a tone of the selected pitch is produced bythe receiver.

By turning the contact arm 26 of theattenuator 21 to the contact point nearest in the circuit to the oscillator, the full voltage of the transformer is applied to the receiver and a loud tone is produced. If this tone produces anr audible sensation the contact arm is moved over the other points therebyv attenua,-v

increasing the amount of ener tion-and correspondingly diminis ing the intensityfof the tone. The rotation of the arm is continued until a position-is reached for which the tone is just perceptible. Interrupting the oscillations at intervals Iby the manipulation of the key 37 assists in the judgment 'of the degree of attenuation needed to produce the just perceptible tone,

intensity in accordance with the principle discussed in the foregoing text. .l

Obviously itis necessary that the subject of the ear analysis should not mani ulate the tone interrupting key' otherwise is attentlon being directed to the manipula- 'y tion of the key would be diverted from the perception of the tone and inaccurate determinations would result. Y

What is claimed is:

1. An electrical oscillator particularly i adapted forl use in apparatus for theanaly-l sis of hearing comprising-an'- amplifying device, a pluralit `of fixed tuned circuits, and circuits includmg keys for connecting said tuned circuits respectively in operative relail tion to said amplifier, the contacts of said keys being so interconnected that the simul-H taneous operation of more than one key prevents the generation of oscillations by `interrupting an essential branch of the oscillator circuit. 2. An electrical oscillator comprising' an amplifying device, a plurality of xed tuned circuits, circuits including keys for y connectin said tuned circuits respectively vin operativerelation'to said amplifier, and

means effective upon the operation of' any l one of said keys to interrupt a-connection` bet-Ween said amplifying .device and all I others of said keys, whereby the-establishment of oscillations of other than the 7desired frequency is prevented". i Y

3. An electrical oscillator comprising an' amplifying device having input terminals and output terminals, va plurality of liXed tuned circuits, keys associated with said tuned circuits respectively, and circuits inj cluding said keys for connecting said tuned x circuits in operative relation to said amplii l lier, said connecting circuits including a circuit connected tocan input terminal of the Y amplifier and passing in. sequence through normally closed contacts in each of saidkeys,l and a circuit connectedto an output terminal of the amplifier passing in the reverse sequence through separate normally closed contacts in said keys, lwhereby upon the operation of any one key the connection is interrupted between the amplifier and all others of said keys.

4. In an apparatus for the analysis of hearing b the determination of the limiting energy ofy sound waves required to produce a sensation of sound, an electrical'oscillator .adapted to generate oscillations ata plu- '115 rality of fixed audio frequencies comprising in-combination an amplifying device, a plurality of xed tuned circuits, keys associated with said tuned circuits respectively,

circuits including said keys for v.connecting 1.20

said tuned circuits in operative relation to -said amplifier and impedances associated respectively with said tuned circuits to adjust to .a uniformintensity the oscillations of the several fixed frequencies.

y In witness whereof, I hereunto subscribe my' name this 22 day of December, A. D. 1923. l

- FRANK-HOWARD GRAHAM., i 

